The present invention relates to an apparatus for scanning a coherent laser beam by relatively moving a hologram which has the function of converging the light beam for the coherent laser beam, and particularly to a light scanning apparatus which is capable of obtaining a desired scanning locus on a desired surface.
The light scanning apparatus according to the present invention can be applied to any system, for example, to an apparatus which reads the bar code printed on a medium such as a price card by scanning it with the light beam, an apparatus for printing letters or figures on a light-sensitive medium by scanning it with a modulated light beam, or into an apparatus which checks complicated printed patterns.
On the other hand, various light scanning apparatuses are already proposed, however those proposed in the U.S. Pat. No. 3,619,033, "Holographic Laser Beam Deflector" by R. V. Pole et al, in Applied Optics Vol. 14, No. 4, April 1975, U.S. Pat. No. 3,953,105, U.S. Pat. No. 4,094,576 and U.S. Pat. No. 4,165,464 are known as light scanning apparatuses for scanning a light beam with comparatively simplified structures.
Namely, the U.S. Pat. No. 3,619,033 describes an apparatus which has the structure that the hologram is arranged on disk, wherewith the laser beam source for reproduction is radiated and the laser beam is scanned through the rotation of the disk.
However, the scanning locus obtained on the medium by scanning the laser beam becomes an arc having a curvature according to the radius of the disk. Therefore such prior art has a disadvantage that the scanning of a straight line or other curve is impossible.
The paper by R. V. Pole et al. introduces the technology wherein a laser beam is radiated from the center of a drum to the cylindrical surface thereof on which the hologram is arranged, and thereby a straight scanning locus is obtained. However, this technology allows the scanning only of straight lines, but not for other freely selected curves. Moreover, it also provides such a disadvantage that preparation of the hologram is difficult because it must be prepared on the drum.
The U.S. Pat. No. 3,953,105 and U.S. Pat. No. 4,049,576 disclose, respectively, an apparatus for scanning the light by arranging hologram on the disk and radiating the laser beam thereto. Moreover, these prior art patents disclose the technology that the scanning locus is compensated using a compensating optical system such as a cylindrical lens, and thereby the desired scanning locus can be obtained.
However, even in this technology, only the curves having the curvature determined by the diameter of the disk can be obtained as a scanning locus obtained by the hologram if no compensating optical system is employed.
Moreover, the U.S. Pat. No. 4,165,464 discloses an apparatus for scanning by radiating the laser beam to the hologram arranged on a rotating disk.
However, this U.S. Pat. No. 4,165,464 also has a disadvantage that a desired curved scanning locus or straight scanning locus cannot be obtained.
Namely, the hologram used for such apparatus is so prepared that the laser beam is converged to a specified converging point. But, since the hologram arranged on the disk rotates in the form of an arc, the converging point also rotates in such a manner as to possess in common the center of the rotating disk. Therefore, the light beam is diffracted on a circle with a radius which is equal to the length between the converging point of the hologram arranged on the disk and the rotating center.